The famous graph that supposedly shows that
recent temperatures are the highest in a thousand years has now been
shown by careful analysis to have been based on faulty data

Marcel Crok

Special to the Financial Post

January 27, 2005

Few people dispute that the earth is getting warmer, but there are
people -- so-called "climate skeptics" -- who question whether the
change is historically unique and whether it is the result of human
activity. These skeptics are generally outsiders, reviled by "true"
climate researchers.

On the one hand, Michael Mann, the first
author of the two noted hockey-stick papers (in Nature in 1998 and in
Geophysical Research Letters in 1999), is the unofficial king of
climate research. In 2002, Scientific American included him as one of
the top 50 visionaries in science. On the other hand, the two Canadian
skeptics are outsiders: Ross McKitrick is a professor of economics and
Stephen McIntyre is a mineral exploration consultant -- which Mann
likes to call a conflict of interest.

Climate skeptics are most
prolific on the Internet, a platform for novices, the scatterbrained
and the experienced alike. Not surprisingly, the climate researchers
whom we consulted (predominantly Dutch) presumed the work of the two
Canadians to be unconvincing. We at Natuurwetenschap & Techniek
were initially skeptical about these skeptics as well. However,
McIntyre and McKitrick have recently had an article accepted by
Geophysical Research Letters -- the same journal that published Mann's
1999 article. This, together with the positive responses of the
referees to that article, quickly brought us around.

Even
Geophysical Research Letters, an eminent scientific journal, now
acknowledges a serious problem with the prevailing climate
reconstruction by Mann and his colleagues. This undercuts both Mann's
supposed proof that human activity has been responsible for the warming
of the earth's atmosphere in the 20th century and the ability to place
confidence in the findings and recommendations of the influential
Intergovernmental Panel on Climate Change (IPCC). The political
implication is a serious undermining of the Kyoto Protocol with its
worldwide agreements on reducing emissions of carbon dioxide and other
greenhouse gases.

In their two seminal papers, Mann and his
colleagues purported to reconstruct Northern Hemisphere temperatures
for the last thousand years. Since 1000, temperatures gradually
decreased (the shaft of the hockey stick), only to increase sharply
from 1900 onwards (the blade).The implication is obvious: Human
interference caused this trend to change. McIntyre and McKitrick merely
attempted to replicate this oft-quoted study. In doing so, they
identified mistake after mistake. They also discovered that this
fundamental reconstruction had never actually been replicated by the
IPCC or any other scientist. In their replication, basically derived
from the same data, temperatures in the 15th century were just as high
as they are today -- an outcome that takes the edge off the alarmist
scenario of anthropogenic global warming. The criticism by the
Canadians is mostly technical in nature: They claim that Mann and his
colleagues have misused an established statistical method -- principal
component analysis (PCA) -- so that their calculations simply mined
data for hockey-stick shaped series and that Mann's results are
statistically meaningless.

The scientists that we consulted did
not immediately recognize the implications of Mann's eccentric method,
suggesting the possibility he himself may not have been aware of the
apparent mistake. However, in response to our inquiries, Mann denies
any errors and rejects any criticism in strident terms.

Up to
January, 2005, none of McIntyre and McKitrick's findings had been
published by major scientific journals. Thus, in the opinion of
established climate researchers, there was no reason to take them
seriously. Climate researchers were quite comfortable in their
consensus and repeatedly referred to this "consensus" as a basis for
policy. The official expression of the consensus comes from the IPCC.
This group, under the flag of the United Nations, comes out with a
bulky report every five years on the state of affairs in climate
research. Hundreds of climate researchers from every corner of the
world contribute to it. In the third report in 2001, Mann himself was a
lead author of the chapter on climate reconstructions.

Mann's
hockey-stick graph was the only climate reconstruction to make it to
the IPCC "Summary for Policy Makers." Its conclusion read: "It is
likely that, in the Northern Hemisphere, the 1990s was the warmest
decade and 1998 the warmest year during the past thousand years." This
statement has been used by governments the world over to promote the
Kyoto Protocol.

Stephen McIntyre first came across the hockey
stick in late 2002. The Canadian government used the graph to promote
the Kyoto treaty. McIntyre explains by telephone: "When I first saw the
graph, it reminded me of dot.com profit forecasts, which were also
hockey sticks. It was a compelling graphic, but, in the mineral
exploration industry, my own field, compelling graphics are one of the
techniques used to interest investors in financing mineral exploration."

McIntyre
has scrutinized promotional graphics and large data sets for years.
"From my own experience, I thought that the graphic looked excessively
promotional," he said. "A trick of mining promoters is to overemphasize
some isolated results. I wondered if this had been the case with the
hockey stick as well. I thought that it would be interesting to look at
the data underlying this graphic -- as though I was looking at drill
core from an exploration project. The interest was simply personal; I
had no intention of writing academic articles and never expected what
happened afterward."

McIntyre sent an e-mail to Michael Mann in
spring 2003, asking him for the location of the data used in his study.
"Mann replied that he had forgotten the location," he said. "However,
he said that he would ask his colleague Scott Rutherford to locate the
data. Rutherford then said that the information did not exist in any
one location, but that he would assemble it for me. I thought this was
bizarre. This study had been featured in the main IPCC policy document.
I assumed that they would have some type of due-diligence package for
the IPCC on hand, as you would have in a major business transaction. If
there was no such package, perhaps there had never been any due
diligence on the data, as I understood the term. In the end, this
turned out to be the case. The IPCC had never bothered to verify Mann,
Bradley and Hughes' study."

Despite billions of dollars spent on
climate research, academic and institutional researchers had never
bothered to replicate Mann's work either. In 2003, McIntyre tackled the
job and, from an unusual hobby, the task has since grown to become
almost a full-time occupation. On an Internet forum for climate
skeptics, he met Ross McKitrick, professor of economics at the
University of Guelph, just outside of Toronto. Since meeting in person
in September of 2003, the two have been working on the project
together. McIntyre does most of the research and McKitrick asks
questions and assists in the writing of papers.

Reliable
temperature measurements have only been available since around 1850.
Before this period, researchers have to rely on indirect indicators, or
"proxies," such as tree rings, ice cores, sedimentary layers and
corals, of which tree rings are the most commonly used. Scientists
studying tree rings will summarize the growth at one site into a single
index or chronology, which might start, for instance, at 1470 and end
at 1980.

Mann's study is the best known of the multi-proxy
studies. For a realistic reproduction of the temperature in the entire
Northern Hemisphere, Mann and others attempt to have a relatively even
geographic distribution of proxies. This posed a difficulty. The
majority of proxies were tree-ring "chronologies," especially from the
U.S. Southwest. To achieve more even geographic distribution (and avoid
being swamped by North American tree-ring data), Mann used principal
component analysis to summarize networks of tree-ring sites, the
largest of which was in North America. The 1998 article reported the
use of 112 proxy series.

However, for some reason, Mann and his
colleagues did not accurately document the data they had actually used.
McIntyre says: "Of the series and sites listed in the original
documentation, 35 were not actually used. To further confuse matters,
in November, 2003, over five years after publication, Mann stated that
they had actually used 159 series, instead of the 112 mentioned in his
Nature article or in Rutherford's e-mail."

We decided to ask Dr.
Eduardo Zorita of the GKSS Research Center in Geesthacht, Germany, who
has also recently examined the calculations behind the hockey stick.
His response: "This is the first time that I've heard of the number
159. In our analysis of the hockey stick, we do not use the actual
data, but a series of pseudo proxies, proxies we take from our
simulations. We have always assumed 112 pseudo proxies."

McIntyre
decided to check the PC calculations for tree-ring networks, by doing
fresh calculations with original data from the World Data Center for
Paleoclimatology (WDCP). His results were very different from Mann's.
He and McKitrick then sent the full data set (originally downloaded
from Mann's FTP site from the address provided by Rutherford) back to
Mann for confirmation that this was actually the data set used. In
response, Mann stated that he did not have the time to answer this or
any other request.

McIntyre and McKitrick then tried to replicate
Mann's Northern Hemisphere temperature calculations from scratch. The
results largely coincided with the hockey stick, except for the 15th
century, when their calculated temperatures were considerably higher
than Mann's and were even higher than corresponding estimates in the
20th century. McIntyre emphasized: "We did not claim to have discovered
a warm medieval period; we only stated that, given the many defects in
the study, it could not be used to assert that the 1990s were the
warmest years of the past millennium."

Their findings were
published in the interdisciplinary journal Energy and Environment in
October, 2003. Mann's early responses were quite unexpected. McIntyre:
"Mann stated that we had used the wrong data and somehow we failed to
notice errors in the data. This was outrageous, as we had downloaded
the data from his own FTP site from the location provided by his own
colleague, Scott Rutherford; we had described countless errors in great
detail and had re-collated over 300 series to avoid these problems.
Now, according to Mann, we should have taken the data off a different
address at his FTP site, but this new address had never been mentioned
in any publication or even on his own Web site."

A little later,
Mann and his colleagues said that they had used a step-wise procedure
to deal with missing data, while McIntyre and McKitrick had not.
McIntyre says: "This was when the figure of 159 series first appeared.
There is no mention of this stepwise method in his Nature article. A
PCA calculation fails if there is any missing data."

But McIntyre
and McKitrick were most intrigued by the attribution by Mann and his
colleagues of the difference in results to three "key indicators" --
most notably a North American data series -- showing that, with
different handling of these three series, they also obtained high
early-15th-century results. McIntyre and McKitrick decided, for the
time being, to concentrate on the years 1400 to 1450, the period with
the biggest discrepancies.

"Mann's own response showed that his
temperature reconstruction for the first half of the 15th-century
depended on [data] from the North American network. We decided to find
out everything that we could about these three indicators."

Because
of the discrepancy between the published methodology and the methods
actually used, the ambiguity over the data sets, and the sudden claim
that 159 series had to be used, McIntyre and McKitrick requested
original source code from Mann in order to fully reconcile their
results. Mann refused. But McIntyre did make an interesting find at
Mann's FTP site -- a Fortran program of about 500 lines for the
calculation of tree-ring series, virtually the only source code on the
entire site. They carefully studied the script and found a highly
unusual procedure that had not been mentioned in the Nature article.

McIntyre
says: "The effect is that tree-ring series with a hockey-stick shape no
longer have a mean of zero and end up dominating the first principal
[data] component; in effect, Mann's program mines for series with a
hockey-stick shape."

At our request, Dr. Mia Hubert of the
Katholieke Universiteit Leuven in Belgium, who specializes in robust
statistics, checked to see if Mann's unusual standardization influenced
the climate reconstruction. She confirms: "Tree rings with a
hockey-stick shape dominate the PCA with this method."

McIntyre
and McKitrick decided to perform another check. Using computer
simulations of so-called "red noise," they generated networks of
artificial tree-ring data over the period of 1400 to 1980. Red noise is
commonly used in climatology and oceanography. McIntyre says: "If we
used Mann's method on red noise, we consistently obtained hockey sticks
with an inflection at the start of the 20th century. We have repeated
the simulation thousands of times and in 99% of the cases, the result
of the PCA was a hockey stick."

Mann's climate reconstruction
methodology would have yielded a hockey-stick graph from any tree-ring
data set entered into the model, as long as there is sufficient red
noise.

The two Canadians are no longer just one voice crying in
the wilderness. On Oct. 22, 2004, in Science, Dr. Zorita and his
colleague Dr. Hans von Storch, a specialist in climate statistics at
the same institute, published a critique of a completely different
aspect of the 1998 hockey-stick article. After studying McIntyre's
finding at our request, Von Storch agrees that "simulations with red
noise do lead to hockey sticks. McIntyre and McKitrick's criticism on
the hockey stick from 1998 is entirely valid on this particular point."